1. Field of the Invention
The present invention relates to a vehicle seat, and more particularly, to a vehicle seat having a back frame assembled with a bracket for reducing a load applied to the neck of an occupant due by shock resulting from a rear collision.
2. Description of the Related Art
There has been known a vehicle seat which can reduce a load to be applied to the neck of an occupant due to shock of a rear collision. For example, a vehicle seat 101 shown in FIG. 5 has a back frame (not shown) assembled with a bracket 130 for suppressing a sinking amount of a waist part of an occupant m into a seatback 103 when a rear collision occurs in a vehicle. Thereby, compared to a configuration where the bracket 130 is not assembled, it is possible to suppress a torso line t of the occupant m sinking into the seatback 103 from being tilted forward, i.e., it is possible to keep a state where the torso line t of the occupant m having sunk into the seatback 103 tilts backward (state shown in FIG. 5(B)). Accordingly, it is possible to suppress an angle (Δθa in FIG. 5(B)) by which a head of the occupant m having sunk into the seatback can be tilted backward. Thus, it is possible to reduce the load to be applied to the neck of the occupant m by the shock of the rear collision (see JP-A-2006-35965).
However, according to the vehicle seat 101 shown in FIG. 5, the bracket 130 is assembled to the back frame such that a surface of the bracket extends substantially vertical direction at a normal posture of the seatback 103 (a posture shown in FIG. 5(A)). When the bracket is assembled as described above, it is not possible to keep the torso line t of the occupant m having sunk into the seatback 103 to be sufficiently tilted backward when a rear collision occurs in the vehicle. In other words, an angle of the torso line t of the occupant m having sunk into the seatback 103 is erected.
Then, since the head of the occupant m is tilted backward until the head comes to into contact with the headrest (in FIG. 5(B), the head is tilted backward by the angle Δθa), a difference (θ1−θ0, in FIG. 5) between an initial angle (θ0, in FIG. 5(A)) formed by the torso line t and the headline h before the rear collision and a first angle (θ1, in FIG. 5(B)) formed by the torso line t and the headline h after the rear collision, i.e., a relative backward tilting angle is increased. Therefore, when the relative backward tilting angle is increased, it is not possible to sufficiently reduce the load that is applied to the neck of the occupant m by the shock of the rear collision.